There are a number of drugs which, owing to chemical instability and poor bioavailability, find only limited uses as a medicament though they have potentially high pharmacological activities. One of means for improving these defects is to provide prodrugs by chemically modifying these drugs.
Japanese Patent Publication (Kokai) No. 57-26684 discloses a useful modifying agent for making such prodrugs consisting of a 1,3-dioxolene-2-one derivative of the formula: ##STR1## wherein R.sub.1 is a hydrogen atom, a lower alkyl or aryl, X is a halogen atom, and R.sub.2 is a hydrogen atom or a hydrocarbon chain forming a ring with R.sub.1. Specific compounds disclosed therein include 4-chloromethyl-5-methyl-1,3-dioxolene-2-one of the formula: ##STR2##